1. Field of the Invention
The present invention is related to an innovative process to produce fine (nano- or submicron-scale) ceramic powder by the glycine-nitrate combustion method through a chemical reactor with the powder collection device.
2. Description of the Prior Art
Nanotechnology is considered as one of the most important industries in 21st century. From consumer products to advanced high-tech areas, there are always applications of nanotechnology. However, due to the limitation of strict manufacturing conditions for nanomaterials, mass production with low cost has not been achieved. Thus, mass production of nanomaterials to reduce cost will be a critical factor to the success of commercialization.
For ceramic materials, in general, the industrial process uses solid-state reaction method. The oxide precursors are mixed first, and then subject to sintering and reaction to form the specific crystal structure required for the product. After that, physical processes like crushing, grinding and dispersing are used to treat the product to a submicron scale. Although such a process can be scaled up for mass production, it usually involves a time-consuming process of high-temperature sintering for crystalline phase formation and it tends to generate impurity phase. Besides, the grinding and dispersing processes to control particle size are very tedious, lengthy and costly. On the other hand, in academic research, sol-gel method is commonly used to synthesize powder. Although this method can obtain purer crystal phase structure, it is limited by the reaction processed in the solvent system and expensive precursors. So mass production based on this method is also difficult. Recently, glycine-nitrate combustion method (GNC) to produce submicron- or nano-scale ceramic powders has been accepted with a great attention. Its general reaction equation can be expressed as follows:xMn++yNO3−+zNH2CH2COOH→aMiOj+bH2O+cCO2+dN2+eO2
in which M represents metals with a charge number of n, and x, y, z, a, b, c, d, e are stoichiometric constants for reactants and products, i, j are the number of atoms in formula. Due to low ignition temperature (about 180° C.), fast reaction and uniform composition, the method is very suitable for producing composite ceramic material with multiple metal components. However, the method also has some drawbacks to hinder its use for mass production. For example, its flare temperature of the instant reaction can be as high as 1400° C. and it is very difficult to collect the powder from reaction due to explosive spillover. Therefore, to commercialize GNC powder manufacturing process, it is necessary to have a sophisticated design of an appropriate reactor to solve the issue of powder loss and improve the yield. The present invention includes an innovative reactor design that can be effectively applied to GNC process to produce fine (nano- and submicron-scale) ceramic powders in a mass-production scale and satisfy the requirements of safety, high yield, and low cost with simple operation.